The trend in the circuit protection industry is currently toward complete circuit protection which is accomplished by the addition of supplemental protection apparatus to standard overcurrent protective devices, such as molded case circuit breakers. U.S. Pat. No. 4,754,247 entitled "Molded Case Circuit Breaker Accessory Enclosure" describes a plurality of accessories that can be field-installed within a circuit breaker without interfering with the integrity of the circuit breaker internal components. This is accomplished by mounting the accessories within a recess formed in the circuit breaker enclosure cover.
An electronic trip actuator which is mounted within the circuit breaker enclosure is described within U.S. Pat. No. 4,679,019 entitled "Trip Actuator for Molded Case Circuit Breakers". The circuit breaker actuator responds to trip signals generated by an electronic trip unit completely contained within a semi-conductor chip such as that described within U.S. Pat. No. 4,589,052. The development of a combined trip actuator for both overcurrent protection as well as accessory function is found within U.S. Pat. No. 4,700,161 entitled "Combined Trip Unit and Accessory Module for Electronic Trip Circuit Breakers". The aforementioned U.S. Patents accordingly represent the advanced state of the art of circuit protection devices.
A more recent example of a combined overcurrent trip actuator and multiple accessory unit is described within U.S. Pat. No. 4,890,184 entitled "Molded Case Circuit Breaker Actuator-Accessory Unit" which combined overcurrent trip actuator and multiple accessory unit also houses the printed wire board that carries the accessory control circuit.
U.S. Pat. No. 4,967,304 describes an electronic circuit interrupter which includes a microprocessor programmed for tailored overcurrent protection to industrial power systems containing a plurality of electric motors as well as motor protective relays or process loops.
In a manufacturing process, various electrical equipment are controlled by means of a process loop DC current usually ranging from 4 to 20 milliamperes. The process loop current is noise-free and transfers through long lengths of wire conductors with minimum losses. To control associated electrical equipment by selective start and stop procedures, the associated electric circuit breakers are turned ON and OFF by means of the process loop current logic.
It would be economically advantageous to incorporate process control logic within the associated circuit breakers to turn the circuit breakers ON and OFF in response to the process loop current without requiring additional process loop current electronics.
One purpose of this invention is to describe a molded case circuit breaker having the capability to detect overcurrent conditions for standard electric circuit protection along with the additional capability of responding to process loop current signals to turn the circuit breakers OFF and ON in response to process control function.